Removable heat sink bumpers on a quad flat package

ABSTRACT

A heat sink for a quad flat package comprises a heat-radiating plate and a plurality of removable bumpers attached to the plate. An area of reduced thickness is disposed at the junction between each bumper and the plate to facilitate removal of the plurality of bumpers from the plate. Preferably, each bumper includes an alignment feature for engaging a complementary feature formed on one of a mounting substrate and a test fixture.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to integrated circuit quad flat packages and particularly to quad flat packages that include a heat sink with bumpers. More particularly, the invention relates to quad flat packages with removable heat sink bumpers.

[0003] 2. Description of the Related Art

[0004] Quad flat integrated circuit packages are known in the art. Moreover, it is known to attach heat sinks with bumpers to the quad flat packages. For example, U.S. Pat. No. 5,808,359 to Muto et al. discloses a quad flat package that includes a heat-radiating metal plate having bumpers formed at the four corners thereof as a unitary structure. Typically, the bumpers on a quad flat package remain with the package to protect the package leads from damage during handling.

[0005] Unfortunately, in conventional quad flat packages, the bumpers take up critical space on a circuit board to which the quad flat package is mounted. The space used by the bumpers could be better used by other components or to reduce the size of the board.

SUMMARY OF THE INVENTION

[0006] The present invention overcomes the above-recited disadvantage by providing a quad flat package having removable heat sink bumpers. According to the invention, a heat sink for a quad flat package comprises a heat-radiating plate and a plurality of removable bumpers attached to the plate. An area of reduced thickness is disposed at the junction between each bumper and the plate to facilitate removal of the plurality of bumpers from the plate. Preferably, each bumper includes an alignment feature for engaging a complementary feature formed on one of a mounting substrate and a test fixture.

[0007] According to one aspect of the invention, the plate is generally square and the plurality of bumpers includes a plurality of bumper hangers and a bumper head coupled to each bumper hanger. The bumper hangers are attached to the plate and extends outwardly from the plate along a diagonal of the plate. The bumper heads include an alignment feature. In a preferred embodiment of the invention, the plurality of bumpers includes four bumpers, with one bumper attached to each corner of the plate and extending outwardly along a diagonal of the plate. The alignment feature preferably includes an aperture formed in each bumper head.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a side view of a quad flat package with a heat sink according to the invention.

[0009]FIG. 2 is a bottom plan view of the quad flat package of FIG. 1.

[0010]FIG. 3 is a section view taken along lines 3-3 of FIG. 2.

[0011]FIG. 4 is a section view taken through a mold for encapsulating a semiconductor circuit on a heat sink to form the quad flat package of FIGS. 1-2.

DETAILED DESCRIPTION OF THE DRAWINGS

[0012] The present invention includes a heat sink 10 attached to a quad flat package 12, as illustrated in FIGS. 1-3. A plurality of leads 14 extend outwardly and downwardly from the quad flat package 12 to connect the package 12 to a circuit board (not shown) or the like.

[0013] As best seen in FIG. 2, the heat sink 10 includes a generally square plate 16 defined by sides 16 a, 16 b, 16 c, 16 d, a top surface 18 (FIG. 1), a bottom surface 20, a plurality of bumper hangers 24 and a plurality of bumper heads 26. Each side 16 a, 16 b, 16 c, 16 d includes a trapezoidal notch 17. Preferably, the heat sink 10 is stamped from a sheet of heat conductive material, but other manufacturing methods and materials can be used.

[0014] Each bumper hanger 24 includes a proximal end 28, attached to a corner of the plate 16, and a distal end 30 attached to a bumper 26. Each bumper hanger 24 advantageously includes a v-shaped notch 34, illustrated in FIGS. 2-3, formed in the bottom surface 20 at the distal end of the bumper hanger 24 and extending partially through the plate 16 toward the top surface 18. The notches 34 allow the bumper heads 26 to be easily removed by bending when the quad flat package 12 is to be installed on a circuit board to provide additional space on the board for other components.

[0015] Each bumper head 26 each includes a distal edge 36, oriented perpendicular to the diagonal, side edges 37, 38, 39, 40, and a central aperture 44. Each side edge 38, 40 is oriented parallel to one of the plate sides 16 a, 16 b, 16 c, 16 d and lies beyond the farthest extent of the leads 14, as illustrated in FIG. 1. Advantageously, the central apertures 44 can be used to align the heat sink with a mounting structure for a mold cavity during the encapsulation process and/or with a test fixture for testing the completed quad package.

[0016] As illustrated in FIG. 4, during fabrication of the quad flat package the heat sink 10 is disposed on a mounting substrate 50. Preferably, a plurality of alignment pins 52 are formed on the substrate 50 and positioned to engage the apertures 44 to accurately position the heat sink 10 with respect to the substrate 50. A semiconductor device 54, with a lead frame 56 attached, is positioned in thermal contact with the heat sink 10, and a mold fixture 60, including upper and lower mold halves 62, 64 that define a mold cavity 68, is positioned to locate the semiconductor device 54 and portions of the lead frame 56 in the mold cavity 68. Encapsulant material 72 is introduced into the mold cavity 68 to encapsulate the semiconductor device 54 and portions of the lead frame 56 to form a quad flat package 12. After the quad flat package 12 is encapsulated, the upper and lower mold halves 62, 64 are removed and the quad flat package 12 is moved to a test fixture (not shown). Again, pins can be formed on the test fixture to engage the apertures 44 to align the quad flat package 12 with the test fixture. After the testing is completed, the bumper heads 26 can be broken off from the heat sink 10 by bending them at the v-shaped notch 34, and the quad flat package 12 is installed on a circuit board (not shown).

[0017] The present invention provides an improved quad flat package that takes up less space on a circuit board and has alignment features to facilitate aligning the package with a mounting substrate and/or a test fixture. Modifications can be made to the invention and equivalents substituted for described and illustrated structures without departing from the spirit or scope of the invention. Accordingly, the scope of the present invention is not to be considered as limited by the specifics of the particular structure which have been described and illustrated, but is only limited by the scope of the appended claims. 

What is claimed as new and desired to be protected by Letters Patent of the United States is:
 1. A heat sink for a quad flat package comprising: a heat-radiating plate; and at least one removable bumper attached to the plate.
 2. The heat sink of claim 1 further including an area of reduced thickness at the junction between the at least one bumper and the plate to facilitate removal of the at least one bumper from the plate.
 3. The heat sink of claim 2 wherein the at least one bumper includes an alignment feature for engaging a complementary feature formed on a mounting device.
 4. The heat sink of claim 1 wherein the plate is generally square and the at least one bumper includes a plurality of bumpers, each bumper including a bumper hanger extending from the plate and a bumper head coupled to the bumper hanger, each bumper head including an alignment feature.
 5. The heat sink of claim 4 wherein the plurality of bumpers includes four bumpers with one of the bumpers attached to each corner of the plate and extending outwardly along a diagonal of the plate, each said bumper head having an aperture as an alignment feature.
 6. A heat sink for a quad flat package comprising: a heat-radiating plate; and a plurality of bumpers extending from the plate, each bumper including an alignment feature for engaging a complementary alignment feature formed on a mounting device.
 7. The heat sink of claim 6 wherein each alignment feature includes an aperture for engaging an alignment pin formed on said mounting device.
 8. The heat sink of claim 6 wherein the plate is attached to a semiconductor package and encapsulating material and each bumper is connected to the plate adjacent the encapsulating material, a notch being formed at each connection to facilitate removal of the bumpers.
 9. The heat sink of claim 8 wherein the encapsulating material lies on the plate and extends beyond the edges of the plate to form a generally square encapsulating member and each bumper includes a bumper hanger extending outwardly from each corner of the plate to a corner of the encapsulating member and a bumper head attached to the bumper, the notch being located at the junction between the bumper head and bumper hanger.
 10. A integrated circuit quad flat package comprising: an integrated circuit; a heat sink coupled to the integrated circuit, the heat sink including a plate and a plurality of removable bumpers, each bumper including a notch for facilitating removal of the bumper; and an integrated package encapsulating said integrate circuit and bonding it to a portion of said heat sink which does not include said removable bumpers.
 11. The quad flat package of claim 10 wherein the integrated package includes a plurality of leads extending therefrom, and the plurality of bumpers includes a plurality of alignment features configured to engage complementary alignment features formed on a mounting device to align the plurality of leads with a plurality of contacts formed on the mounting device.
 12. The quad flat package of claim 11 wherein the plurality of alignment features includes an aperture formed in each bumper.
 13. The quad flat package of claim 10 wherein the plate is generally square and the integrated package includes a generally square encapsulating member, the plate further including a plurality of corners and each bumper including a bumper hanger and a bumper head, one bumper hanger extending outwardly from each corner of the plate to a corresponding corner of the encapsulating member, the notch being disposed adjacent the corner of the encapsulating member.
 14. A method for forming a quad flat package comprising the steps of: forming a heat sink having a plate portion and a plurality of bumpers extending from the plate portion, the plate portion being configured to receive an encapsulated package; forming a notch in each bumper to enable each bumper to be removable from said heat sink; placing an integrated circuit in contact with the heat sink; and encapsulating said integrated circuit with an encapsulating material such that said encapsulating material is in contact with a portion of said heat sink which does not include said bumpers or notches.
 15. The method of claim 14 wherein the step of forming a heat sink includes the step of forming an alignment feature in each bumper.
 16. The method of claim 15 wherein the alignment feature includes an aperture for receiving an alignment pin.
 17. A method for forming a quad flat package comprising the steps of: forming a heat sink having removable bumpers; encapsulating a semiconductor package; and securing the encapsulated package to the heat sink.
 18. The method of claim 17 wherein the step of forming the heat sink includes the step of forming a plate portion and a plurality of bumpers extending from the plate portion, each bumper including a bumper hanger and a bumper head joined to the bumper hanger.
 19. The method of claim 18 wherein the step of forming a plate portion and a plurality of bumpers includes the steps of forming an aperture in each bumper head and forming a notch in each bumper hanger at a point adjacent the encapsulated package.
 20. The method of claim 17 wherein the encapsulation of said semiconductor package secures said encapsulated package to said heat sink. 